1. Field of the Invention
The present invention relates to a fluorescent lamp, and more particularly, to a fluorescent lamp for a backlight unit in a liquid crystal display (LCD) device and a method of fabricating the fluorescent lamp.
2. Discussion of the Related Art
With development of the information society, flat panel display (FPD) devices have been developed and widely utilized as substitutes for cathode ray tube (CRT) devices because the FPD devices have light weight, thin profile, and low power consumption characteristics. Generally, display devices are classified into emissive display devices and non-emissive display devices according to their ability for self-emission. The emissive display devices display images by taking advantage of their ability to self-emit light, whereas the non-emissive display devices require light sources since they do not emit light by themselves. For example, plasma display panel (PDP) devices, field emission display (FED) devices, and electroluminescent display (ELD) devices belong to the emissive display devices. The LCD devices, which are usually categorized as non-emissive display devices, are widely utilized in notebook and desktop computers because of their high resolution, capability of displaying color images, and high quality image display.
The LCD device includes an LCD module that is provided with an LCD panel for displaying images and a backlight unit for supplying light to the LCD panel. The LCD panel includes two substrates facing and spaced apart from each other, and a liquid crystal layer interposed therebetween. The liquid crystal layer includes liquid crystal molecules that have a dielectric constant and refractive index anisotropic characteristics because of their long, thin shapes. In addition, two electrodes for generating an electric field are formed on the two substrates, respectively. Accordingly, an orientation alignment of the liquid crystal molecules can be controlled by supplying a voltage to the two electric field generating electrodes, thereby changing transmittance of the LCD panel based on polarization properties of the liquid crystal molecules. However, the LCD panel belongs to a non-emissive-type display device, and needs an additional light source. Thus, the backlight unit is disposed under the LCD panel as the light source. In particular, the LCD panel displays images using light produced by the backlight unit.
In general, the backlight units are either edge-types or direct-types, according to the disposition of the light sources. As display areas of the LCD devices become increasingly large, the direct-type backlight units, including a plurality of light sources, are usually utilized to provide high brightness.
A fluorescent lamp, used as the light source of the backlight unit, is a cold cathode fluorescent lamp (CCFL). The CCFL includes a glass tube and an external electrode that extends from an end portion of the glass tube. However, with respect to a large size LCD panel, using the CCFL as an the edge-type backlight unit fails to provide adequate brightness because it fails to evenly distribute light to the large size LCD panel. On the other hand, the CCFL can be used as a direct-type connected as a parallel arrangement; however the CCFL is not driven using just one inverter. Thus, the number of the CCFLs restricts proper brightness of the LCD panel. Therefore, a reflector having a predetermined configuration is necessary, and a distance between a diffusion plate and the CCFL should be set long enough to obtain a uniform brightness, thereby causing an increase in the thickness of the LCD panel.
Accordingly, with respect to a large size LCD panel with high brightness and high efficiency, an external electrode fluorescent lamp (EEFL) is utilized to provide a long life and light weight for the LCD panel. The EEFL may be a belt type, a cap type or an expanded type. The expanded type EEFL includes a glass tube that has both end portions swelled out.
FIG. 1 is a schematic view illustrating a cold cathode fluorescent lamp (CCFL) according to the related art. FIG. 2 is a schematic view illustrating an external electrode fluorescent lamp (EEFL) according to the related art.
As shown in FIG. 1, a CCFL 5 includes a tube 1 filled with a discharge gas and a fluorescent material, an internal anode electrode 3a and an internal cathode electrode 3b in both inner edges of the tube 1, respectively. On the other hand, as shown in FIG. 2, an EEFL 15 includes a tube 10, an external anode electrode 13a and an external cathode electrode 13b that cover both outer edges of the tube 10, respectively.
The CCFL 5 has a disadvantage in that if the CCFL 5 is turned on frequently, its lifetime may be reduced due to damage to the internal anode electrode 3a and the internal cathode electrode 3b exposed mercury (Hg) molecules. In addition, when the CCFL 5 is applied to the edge-type backlight unit, although the CCFL 5 itself has high brightness, brightness of the LCD panel utilizing the CCFL 5 is low. For this reason, the edge-type CCFL is undesirable for use in an LCD panel. Similarly, when the CCFL 5 is applied to the direct-type backlight, multiple CCFLs 5 are arranged in a row and cannot be driven by one inverter.
The EEFL 15 of FIG. 2 has higher brightness, higher efficiency, longer lifetime, and a slimmer profile in comparison with the CCFL 5 of FIG. 1. However, the external anode electrode 13a and the external cathode electrode 13b of the EEFL 15 should have a predetermined length so as to maintain a minimum energy to excite electrons. This results in difficulty obtaining a desired bezel portion.
Recently, the lamps of the EEFL 15 have not been connected in a row so that each lamp is connected to each inverter. Thus, a light intensity of the lamp may be independently controlled, but the total size of the LCD device is increased. As a result, it is difficult to provide an LCD device with light weight and a thin profile.